The present invention relates to a sputtering target with low generation of sparticles and to process for producing same.
The sputtering method is a well-known technique as a means for forming a thin film. The basic principle thereof is to apply voltage between a substrate (anode side) to which the thin film is to be formed and a target (cathode side) facing the substrate at a close distance and which is formed from a thin film forming substance, so as to change argon gas into a plasma. As a result, the argon ions generated thereby collide with the target, which is a cathode material, the energy thereof discharges (knocks out) the target material outside, and the discharged material is laminated on the opposed substrate face.
A thin film forming device employing this sputtering principle includes various modified types such as a bipolar bias sputtering device, high frequency sputtering device, plasma sputtering device, but these devices employ the same basic principle.
The material for forming the thin film is referred to as a target, since it becomes the target of the argon ions. Since this target is formed from the collision energy of ions, the thin film forming material constituting the target is laminated on the substrate in an atomic form, or a cluster form formed from an aggregate of such atoms. As a result, a fine and accurate thin film can be formed, and this is the reason it is being widely used in various electronic components today.
Recently, this sputtering used for forming thin films is being demanded of extremely sophisticated deposition methods, and an important task is to form films with few defects.
The generation of such defects in this sputtering is not only attributable to the sputtering method, but is also often caused by the target itself. As such a cause of the generation of defects resulting from the target, there is the generation of particles and nodules.
In normal conditions, the material sputtered (discharged) from the target will adhere to the opposed substrate, but the material is not necessarily sputtered perpendicularly, and is discharged in various directions. This kind of discharged material will adhere to the components inside the sputtering device other than the substrate, and this at some point will peel off, float, and reattach to the substrate.
This kind of material is referred to as particles, and this is not an originally scheduled thin film forming material. Further, since such particles often adhere as a large cluster, for instance, these particles will cause a short circuit in the fine wiring film of electronic components, and lead to the generation of defective products. In the generation of such particles, it has been discovered that the generation of particles will increase or decrease depending on the degree of materials discharged from the target; that is, the surface condition of the target.
Further, generally, the target face material is not reduced (eroded) evenly due to the sputtering, but there is a tendency that a specific area, a ring shape for example, is eroded depending on the inherent characteristics of the constituent material and sputtering device, and on method of applying voltage. Moreover, depending on the type of target material or the production method of the target, a protrusive substance with numerous bumps known as nodules is formed on the target surface.
Since this is one of the thin film forming materials, it will not directly affect the thin film. Nevertheless, minute arcs (microarcing) will occur to the protrusions of the nodules, and it has been observed that this results in the increase of particles.
Recently, a target is not formed from a uniform material, and is often used in a state where oxides, carbides, nitrides, borides, intermetallic compounds, carbonitrides, and other substances are mixed in a matrix phase made of a ductile material. Here, a problem of increase in the generation of nodules and particles arises.
As conventional technology, disclosed is a sputtering target in which the processing defect layer (fracture layer) containing minute cracks and defective parts arising during the machine work is removed from the surface of a high-melting point metal alloy sputtering target (c.f. Patent Document 1); and a technique for uniformizing the film and suppressing the generation of nodules and particles by adjusting the surface roughness of the sputtering target so as to reduce the amount of residual contamination, hydrogen content on the surface, and thickness of the affected layer (c.f. Patent Document 2).
Nevertheless, although these technologies anticipate that the generation of nodules and particles will considerably affect the surface condition of the target, the actual situation is that they are unable to resolve the existing problems.
Moreover, technology is disclosed for inhibiting the generation of initial arcing in an ITO sputtering target by covering the surface, which was subject to grinding and polishing, with ITO as the same material as the target (Patent Document 3). Nevertheless, this technology is characterized in coating the same material, and can only be achieved with ITO. In addition, this technology fails to solve the problems in severe conditions where oxides, carbides, nitrides, borides, intermetallic compounds, carbonitrides, and other substances without ductility exist in the target.
[Patent Document 1] Japanese Published Unexamined Application No. H3-257158
[Patent Document 2] Japanese Published Unexamined Application No. H11-1766
[Patent Document 3] Japanese Published Unexamined Application No. 2003-89868